Operation Longlife — E. Hoffmann Price

In the 21st century, Avery Jarvis "Doc" Brandon lived in luxurious seclusion on subtropical Nameless Island. An immensely wealthy gene-engineer who dabbled in illegal baby-making, Doc was 186 years of age and looked 35. But a storm loomed on the horizon. Bureaucrats had blundered across Doc's real age. They wanted his "secret discovery" and would undertake anything -- including kidnapping, blackmail, and murder -- to get it!